AlCl3-Mediated Aldol Cyclocondensation of 1,6-and 1,7-Diones to Cyclopentene and Cyclohexene Derivatives

Exactly 1/3 mol of AlCl3 is sufficient to cyclize 1 mol of 1,omega-dibenzoylbutane (or pentane) to a cyclopentenone (or hexenone) derivative in high yield at room temperature in 40 min to several hours. This condensation is driven by removing elements of water as HCl and Al(OH)(3), and the product enones are exclusively unconjugated, unlike the base-catalyzed condensations providing thermodynamically more stable conjugated enones.